The present invention relates in general to sound transducers, and in particular to a new and useful dynamic loudspeaker which utilizes a magnetic liquid sealed in a gastight space to avoid deterioration in the characteristics of the loudspeaker.
Dynamic loudspeakers are known (Instra. A. Control Syst. 48, 1975, 10 pages 41 to 44), which includes air space in which the voice coil of the dynamic system is movable. The space is designated an "air gap" of the magnetic pole case and is filled with a magnetic liquid. The magnetic liquid is held in place in the gap by the permanent magnetic field of the magnetic pole case. The liquid serves the purpose of improving the acoustic properties, particularly the distortion factor and the phase delay of the loudspeaker system. Also, the manufacture of the loudspeaker is simplified since the dimensional variations allowable in manufacture take on a less significant effect. The filling imparts properties to the "air gap" which are close to properties of the magnetic poles themselves. The air gap is thereby reduced to zero, as intended.
Another substantial advantage over dynamic systems without a filled air gap are improved thermal conditions. As compared to air, the thermal conductivity of the magnetic liquid is very much higher, so that resistance to heat transmission between the coil and the magnetic pole case is reduced. This increases the maximum admissible input power, considered at equal maximum temperatures of the moving coil.